Electroluminescent mark sensing



June 4, 1963 G. R. ADAMS ETAL 3,092,726

ELECTROLUMINESCEN'I' MARK SENSING Filed Dec. 31, 1956 Phofosensi fiveDetector M Transparent Conductive 9 Coahng l Electrode I Pofe nfiol ISource Photosensitive 5 Detector INVENTORS G. R Adams T. R. Cfeary AGENTUnited States Patent 3,092,726 ELECTROLUMINESCENT MARK SENSING GeorgeRichard Adams, Elkins Park, and Thomas R- Cleary, Drexel Hill, Pm,assignors to Sperry Rand Corporation, New York, N.Y., a corporation ofDelaware Filed Dec. 31, 1956, Ser. No. 631,770 1 Claim. (Cl. 250-219)The present invention relates to an improved method and apparatus formark sensing such as may be employed, for instance, in readingdocuments, and is more particularly concerned with a system of mark ordocument sensing employing electroluminescent phosphors, whereby morecertain mark sensing may be achieved than has been the case heretofore.

It is well known at the present time that information may be placed upona document, for instance similar to a punch card, by disposing aplurality of spaced marks comprising fluorescent or phosphorescentmaterial on the document, said marks being spaced in accordance with apreselected code. Marks of this general type are ordinarily sensed bystimulating and/or exciting the phosphorescent materials comprising themarks, for instance by means of a source of ultra-violet radiation,whereby the marks emit light which may be detected by an appropriatephotosensitive structure. It has been found that document sensingsystems, utilizing substantially conventional phosphorescent orfluorescent materials, may often give an incorrect indication ofinformation on a document of card, by reason of the accidental orinadvertent introduction of extraneous luminescent materials on thedocument; and these extraneous materials are excited along with themarks and emit light, whereby an incorrect determinatiion of theinformation on the document can occur.

The present invention serves to obviate this difficulty of known sensingsystems, and provides a system which is inherently safe from spurious ornoise signals due to the excitation of most extraneous luminescentmaterials which may be present on or in a document being sensed. As willappear subsequently, this improved document sensing is accomplishedprimarily through the use of marks comprising electroluminescentphosphors, and more particularly those known to exhibit the phenomenonof intrinsic electrolumines-cence, i.e. luminescence in response toexcitation by an electric field.

It is accordingly an ob ect of the present invention to provide animproved mark sensing arrangement.

Another object of the present invention resides in the provision of animproved method and apparatus for mark sensing utilizingelectroluminescent phosphors.

Still another object of the present invention resides in the provisionof a mark sensing system which is inherently safe from incorrectinformation sensing due to the presence of false marks or extraneousluminescent materials on or in the document being sensed.

Another object of the present invention resides in the provision of adocument sensing system which is more certain in its operation thansystems suggested heretofore.

A further object of the present invention resides in the provision of animproved document having marks of electroluminescent phosphors thereon,as well as in the provision of an improved method and apparatus forreading such documents.

A further object of the present invention resides in practicalutilization of the fact that electroluminescent marks can be moreconveniently sensed while they are being excited than can ultra-violetexcited fluorescent marks.

A further object of the present invention resides in practicalutilization of the fact that electroluminescent marks can be read whilefully excited whereas phosphorescent marks read during their after-glowperiod are not radiating as much energy as they were when under theexciting radiation. The mode of excitation contemplated by the presentinvention furthermore consumes less power than does excitation ofluminescent materials by ultra-violet lamps.

In providing for the foregoing objects and advantages, the presentinvention contemplates the provision of documents having informationstored thereon in a pattern of electroluminescent phosphor marks. Aswill appear subsequently, the number of naturally occurring or syntheticmaterials which exhibit electroluminescence is relatively small, wherebythere is little likelihood that fialse or ex- *traneous marks of suchelectroluminescent phosphors could occur in or upon the document.

The electroluminescent phosphor marks are caused to be read from thedocument by properly exciting the marks; and in particular, thisexcitation is accomplished in accordance with the present invention bysubjecting the marks to an electric field. Proper excitation of theelectroluminescent marks, in accordance with the present invention,requires that the electric field be changing in the marks. This changingfield etfect may be accomplished, as will appear subsequently, byimposing a varying electric field upon either a stationary or movingdocument containing the marks; or, in the alternative, by moving thedocument across the boundary of a substantially constant electric field.Since only a relatively few materials are responsive to an electricfield to emit radiant energy, the likelihood of false sensing due toextraneous material in or on the document is materially reduced.

The foregoing objects, advantages, construction and operation of thepresent invention will become more readily apparent from the followingdescription and accompanying drawing.

In particular, referring to the drawing, it will be seen that inaccordance with the present invention, an improved rnethod and apparatusfor document sensing may utilize an improved document 10, for examplesimilar to a punch card, having one or more groups of marks 11 disposedthereon in accordance with a preselected pattern or code. The severalmarks 11 comprise, in accordance with the present invention,electroluminescent phosphors carried on or in the document 10. Typicalmateriazls which may be utilized in the provision of marks 11 includezinc sulfide, zinc oxide, zinc selenide, cadmium sulfide, cadmiumselenide, and mixtures thereof, activated with copper, manganese,aluminum, silver, or mixtures thereof.

Electroluminescent phosphors, of the comprising marks 11, may be excitedby subjecting those marks to an electric field, and in particular, suchmarks may be excited to emit light by eifecting a changing electricfield in the marks. Accordingly, the document 10 is utilized inconjunction 'with a reading apparatus comprising a pair of spaced,substantially parallel electrodes 12 and 13. Document 10 may be causedto pass between said electrodes 12 and 13 by 'means of appropriate drivemeans schematically illustrated as rollers 14 and motor 15. It will beappreciated that various drive means may be employed; and it willfiurther \be appreciated from the subsequent description that the marks11 can be read when the document 10 is either moving or stationary,provided proper attention is given to the manner of exciting thosemarks.

In accordance with one form of the invention, the electrode 12 cancomprise a metal or conductivr isheet, while the electrode 13 comprisesa tnansparent sheet, e.g. glass, having a transparent conductive coating16, e.g. an oxide of tin, on a surface thereof. This particulararrangement senses the marks 11 by reason of the light emitted fromthose marks passing through the tnansparent sheet 13. Due to the opacityof sheet 12 no light can pass in a downward direction. In thealternative, however, it will be appreciated that both of electrodes 12and 13 can comprise transparent materials having transparent conductivecoatings thereon, in which event marks similar to 11 can be disposed onboth sides of document 10.

Excitation of the marks 11 is accomplished under the control of apotential source 17, the output of which is coupled respectively toconductive electrode 12 (or to the conductive coating thereon), and tothe conductive coating 16 on electrode 13. As a practical matter,electroluminescent phosphors of the types comprising marks 11 areexcited only when the electric field appearing between electrodes 12 and13, due to application of potential from source 17, is changing in marks11. This changing field may be achieved by having the source 17 producean A.C. output potential; and the application of the resulting changingelectric field to marks 11 will excite the marks and cause them to emitlight, regardless of whether document 11) is moving or stationary. Inthe alternative, however, the potential source 17 may produce a DC.potential output, thereby to effect a substantially constantelectrostatic field between electrodes 12 and 13, in which event marksensing occurs so long as document and marks 11 thereon are caused tomove across the boundary of that constant electric field. In eitherevent, however, the desired electric field is effected in the markswhereby the electroluminescent phosphors comprising marks 11 are causedto emit light.

Light so emitted from marks of an electric or electrostatic fieldthereto, is detected by a photosensitive detector 18 comprising, in theexample illustrated, a plurality of spaced photocells, and if desired,shield means may be interposed between the several photocells comprisingdetector 18 to assure that each responds only to light emitted by marksin a given position on document 10. In addition, if desired, an opticalsystem 19 may be interposed between electrode 13 and photosensitivedetector :18. This optical system may take the form of a lens, asillustrated, or may be more complex in nature, depending upon therequirements of a particular system. In the alternative, however,optical system 19 may be eliminated, provided the level of lightemission from the several marks is suificiently high, and provided thearea over which each mark emits light is sufficiently confined to permita proper sensing to occur.

In the event that electrode 12 comprises a transparent material, sensingof marks on both sides of the document could, if desired, beaccomplished; and in this latter form of the invention, a furtherphotosensitive detector 20 analogous to detector 18 could be disposed onthe opposite side of document 10, as illustrated.

It will be appreciated from the foregoing, that excitation of marks 11is accomplished by subjecting those marks to an electric field which ischanging in the marks; and it will further be appreciated that onlythose marks which comprise electroluminescent phosphors will be causedto emit light upon excitation by the aforementioned field. While theelectroluminescent phosphors comprising marks 11 do respond toexcitation by ultraviolet, it should be further noted that conventionalphosphors ordinarily excited by ultra-violet do not respond to anelectric field in the manner described.

Accordingly, it is preferable to provide a light-tight housing 21 aboutthe reading apparatus to assure that ultra-violet, and radiant energy ofthe same wavelength as the marks emit, is positively excluded from thesensing region. As a practical matter, relatively little ultra-violetradiation will be present within a building structure, but the housing21 is nevertheless preferably provided in order to assure that the onlyform of excitation applied to the electroluminescent phosphors placed ondocument 10 11 upon the application is an electric field, whereby theonly light detected is that emitted by the excited electroluminescentphosphor marks 11. This arrangement thus eliminates, for all practicalpurposes, extraneous emissions due to spurious foreign materials whichmay be present on or in document 10, whereby document sensing inaccordance with the present invention provides a more certain andaccurate information output than has been possible heretofore.

While we have thus described a preferred embodiment of the presentinvention, many variations will be suggested to those skilled in theart, and it must therefore be emphasized that the foregoing descriptionis meant to be illustrative only, and should not be consideredlimitative of our invention. For instance, while transparent electrodessuch as 13 (and/or 12) have been discussed in detail, such structuresare not in tact essential. The prime consideration of the presentinvention, in this particular respect, is that the marks be subjected toan electric field whereby said marks emit light, in combination withmeans for detecting the light so emitted. Accordingly the electrodes,rather than being of a planar transparent material, could take the formof a grid of wires, for example, in which event light passing throughspacings between the wires comprising said grid could be detected byappropriate photosensitive structures. Still other modifications will beapparent to those skilled in the art. All such modifications andvariations as are in accord with the principles of the present inventionare therefore meant to fall within the scope of the appended claim.

Having thus described our In an information sensing system, thecombination of a document bearing a coded pattern of spacedelectroluminescent phosphor marks, a pair of substantially parallelelectrodes, a potential source connected to said electrodes forproducing an electric field therebetween, roller means for moving saiddocument into, through and out of said electric field, a plurality ofphotocells tor detecting the light emitted from said encoded phosphormarks, said photocells being arranged to detect corresponding phosphormarks in given positions on said document, an optical system forfocusing on said photocells the light emitted from said phosphors, and alight tight housing enclosing said electrodes whereby phosphors on saiddocument are excited only by said electric field.

References Cited in the file of this patent UNITED STATES PATENTSinvention, we claim:

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